Elasticsearch Elasticsearch Long Running Search Task Issues

By Opster Team

Updated: Jul 4, 2023

| 2 min read

What does this mean?

A long running search task in Elasticsearch refers to a search query that takes an unusually long time to complete. This can be due to various reasons, such as complex queries, large data sets, or insufficient resources. 

When  Opster AutoOps detects a long running search task, it raises an event to notify the user about the potential issue, providing personalized recommendations for your own system. You can also configure notifications to avoid this issue forming in the future.

Why does this occur?

There are several reasons why a long running search task may occur in Elasticsearch:

  1. Complex queries: If the search query is too complex or involves multiple aggregations, it may take longer to execute.
  2. Large data sets: Searching through a large amount of data can cause the search task to take longer than expected.
  3. Insufficient resources: If the Elasticsearch cluster does not have enough resources (CPU, memory, or disk space), it may struggle to complete the search task in a timely manner.
  4. High cluster load: If the cluster is already under heavy load due to other tasks, it may cause the search task to take longer to complete.

Possible impact and consequences of long running search tasks

The impact of a long running search task can be significant, as it may affect the overall performance and stability of the Elasticsearch cluster. Some potential consequences include:

  1. Slower search performance: Other search queries may experience slower response times due to the resources being consumed by the long running search task.
  2. Reduced cluster stability: The cluster may become less stable as it struggles to handle the additional load from the long running search task.
  3. Increased resource usage: The long running search task may consume more resources than necessary, leading to increased costs and potential resource exhaustion.

How to resolve

To resolve the issue of a long running search task in Elasticsearch, consider the following recommendations:

1. Identify the long running search tasks: Use one of the following commands to list all search tasks currently running in the cluster. Note that the first one is a bit more condensed and tasks are sorted by the longest running tasks first, so it’s easier to spot them:

GET _cat/tasks?v&detailed=true&actions=*search*
GET /_tasks?detailed=true&actions=*search*

2. Cancel the long-running search tasks: Use the following command to cancel the long-running search tasks and improve the cluster stability:

POST /_tasks/<task_id>/_cancel

Replace `<task_id>` with the ID of the long-running search task you want to cancel.

3. Optimize search queries: Review and optimize the search queries to reduce their complexity and improve their performance.

4. Increase cluster resources: Allocate more resources (CPU, memory, or disk space) to the Elasticsearch cluster to handle the search tasks more efficiently.

5. Monitor cluster load: Regularly monitor the cluster load and adjust the resources or queries accordingly to prevent long running search tasks from occurring.


By understanding the meaning, causes, and potential impact of a long running search task in Elasticsearch, you can take appropriate steps to resolve the issue and maintain the performance and stability of your Elasticsearch cluster.

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